The Collaborative International Dictionary of English v.0.48:

Ketch \Ketch\ (k[e^]ch), n. [Prob. corrupted fr. Turk.
   q[=a][imac]q : cf. F. caiche. Cf. Ca["i]que.] (Naut.)
   1. An almost obsolete form of sailing vessel, with a mainmast
      and a mizzenmast, -- usually from one hundred to two
      hundred and fifty tons burden.
      [1913 Webster]

   2. (Naut.) In modern usage, a sailing vessel having two
      masts, with the main mast taller than the aftermost, or
      mizzen, mast.
      [RDH]

   Bomb ketch. See under Bomb.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ketch \Ketch\, n.
   A hangman. See Jack Ketch.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ketch \Ketch\, v. t. [See Catch.]
   To catch. [Now obs. in spelling, and colloq. in
   pronunciation.]
   [1913 Webster]

         To ketch him at a vantage in his snares. --Spenser.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ketch
    n 1: a sailing vessel with two masts; the mizzen is forward of
         the rudderpost